In a computer, as typified by a server in a computer network system, etc., temperature rises as the operation of a CPU or a memory proceeds. In particular, due to recent advances in CPU performance, the temperature rise is noticeable. In order to prevent such a temperature rise, a method is generally employed in which a cooling fan is provided in the computer such as server, etc. so as to cool the inside of the computer.
However, a rotation of the cooling fan, which generates noise, is one of the major noise source of the computer such as server. In general, the fan rotation speed is controlled taking the computer's peak load state into consideration, so that the fan rotation speed in the low load state of the computer is excessively high in terms of cooling purpose, and noise is unnecessarily loud.
In view of the above point, a method for reducing noise of a cooling fan for a computer used as communication control device is proposed (refer to, e.g., PTL 1).
Further, PTL 2 discloses a technique that provides a temperature sensor for a CPU and rotates a cooling fan at a rotation speed previously set as the maximum allowable rotation speed for the temperature detected by the sensor. In this technique, the CPU clock is controlled so as to perform sufficient cooling of the computer with the set rotation speed of the fan. With this technique, it is possible to provide user's desired quietness.